1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a thermal ink-jet printhead that is able to filter impurities and reduce an amount of time necessary to refill an ink chamber.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined image, color or black, by ejecting a small volume droplet of ink at a desired position on a recording sheet. Inkjet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermal ink-jet printhead, in which heat is applied to form and expand a bubble in ink to cause an ink droplet to be ejected due to the expansion force of the formed bubble. A second type is a piezoelectric ink-jet printhead, in which an ink droplet is ejected by a pressure applied to the ink due to a deformation of a piezoelectric element.
A thermal ink-jet printhead is classified into a top-shooting type, a side-shooting type, and a back-shooting type depending on a bubble growing direction and a droplet ejection direction. In a top-shooting type of printhead, bubbles grow in the same direction in which ink droplets are ejected. In a side-shooting type of printhead, bubbles grow in a direction perpendicular to a direction in which ink droplets are ejected. In a back-shooting type of printhead, bubbles grow in a direction opposite to a direction in which ink droplets are ejected.
An ink-jet printhead using the thermal driving method should satisfy the following requirements. First, manufacturing of the ink-jet printheads should be simple, costs should be low, and should facilitate mass production thereof. Second, in order to obtain a high-quality image, cross talk between adjacent nozzles should be suppressed while a distance between adjacent nozzles should be narrow; that is, in order to increase dots per inch (DPI), a plurality of nozzles should be densely positioned. Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after ink has been ejected from the ink chamber should be as short as possible and the cooling of heated ink and heater should be performed quickly to increase a driving frequency.
An ink droplet ejection mechanism of a thermal ink-jet printhead will now be explained in detail. When a pulse current is applied to a heater, which includes a heating resistor, the heater generates heat and ink near the heater is instantaneously heated to approximately 300° C., thereby boiling the ink. The boiling of the ink causes bubbles to be generated, and exert pressure on ink filling an ink chamber. As a result, ink around a nozzle is ejected from the ink chamber in the form of a droplet through the nozzle.
Once the bubbles burst and ink is ejected, an ink chamber requires a supply of an equal amount of new ink, which flows through an ink channel. The ink channel necessarily creates some resistance against the flow of the ink. Accordingly, the ink channel should be designed to reduce ink flow resistance while ink is flowing into the ink chamber. However, the ink channel should be designed to adjust the ink flow resistance to be sufficiently high to prevent the ink from flowing reversely, i.e., back flowing, when the ink droplet is ejected through the nozzle. Accordingly, the ink flow resistance of the ink channel and the nozzle require proper adjustment in consideration of the mobility of an ordinary ink droplet and the time necessary to refill the ink chamber.
FIG. 1 illustrates a conventional ink-jet printhead capable of filtering impurity particles. Referring to FIG. 1, ink is supplied to heaters 401 and 403 from a manifold 407 through ink channels 409, 411, 413, and 415. In this conventional configuration, the ink-jet printhead employs islands 417, 419, 423, 425, 427, 429, and 431, which are formed in ink paths using a photoresist, to prevent impurity particles 433 and 435 from reaching the heaters 401 and 403.
While this conventional ink-jet printhead, constructed as described above, is able to prevent the ink paths from being blocked with impurities, this printhead is not able to adjust ink flow resistance during an ink refill operation, i.e., during the time from when the ink droplet is ejected until the ink chamber is refilled.
Another conventional ink-jet printhead incorporates a porous material into an ink channel. It is known that the flow resistance of a porous material is proportional to the square of the velocity of the flow. Thus, an ink channel made of a porous material has an advantage in that when ink is ejected and fluid velocity is high, a flow resistance increases, and when ink is refilled and fluid velocity is low, a flow resistance decreases. However, such an ink-jet printhead using the porous material has high manufacturing costs and requires complex manufacturing processes.
Still another conventional ink-jet printhead includes a structure to filter impurities before ink is introduced into an ink chamber. However, in such a structure, an ink channel and a filter must be individually constructed.